1. Field of the Invention
The present invention relates to a semiconductor device (semiconductor chip) that achieves a desired function when connected to a semiconductor device (semiconductor chip) having a predetermined function so as to be functionally complemented or enhanced thereby, and the present invention relates also to a semiconductor device that is built by connecting together a plurality of semiconductor devices (semiconductor chips) having such a relationship with one another.
2. Description of the Prior Art
Some semiconductor devices achieve desired functions by the use of a plurality of semiconductor chips. A typical example is semiconductor devices that are built by superposing a plurality of semiconductor chips on one another and bonding them together and that thus have chip-on-chip structures.
In this type of semiconductor device, the internal circuit 111 of the mother chip 110 is often designed as an incomplete or insufficient circuit that does not achieve any practical function on its own; that is, this internal circuit 111 is often designed to achieve a desired practical function only when it is functionally complemented or enhanced by the internal circuit 121 of the daughter chip 120. Specifically, for example, the output signal of the internal circuit 111 of the mother chip 110 is fed via the bump 130 to the internal circuit 121 of the daughter chip 2, then the output signal of this internal circuit 121 is fed via the bump 131 back to the mother chip 110, and only then this signal is fed to the external connection pad 121 as a practically significant signal.
The manufacturing process of a semiconductor device imperatively includes steps for functional checking of the semiconductor device, which involve pressing a test probe onto the pads provided on the surface of the semiconductor device. A semiconductor device composed of a plurality of semiconductor chips, if found defective after assembly, cannot be saved from being discarded totally, and therefore it is desirable to conduct functional checking of the individual semiconductor chips constituting such a semiconductor device before assembly.
However, as shown in FIG. 4, in a semiconductor device having a chip-on-chip structure that is built by bonding together a mother chip 110 and a daughter chip 120 with bumps 130 and 131 between them in such a way that the surface of the mother chip 110 faces the surface of the daughter chip 120, the internal circuit 111 of the mother chip 110 is connected to the internal circuit 121 of the daughter chip 120 by way of those bumps 130 and 131. External connection pads 112 for allowing input/output of signals from/to an external device are usually provided near the edge of the surface of the mother chip 110 so as to avoid the region thereon in which the daughter chip 120 is bonded to the mother chip 110.
In this case, the internal circuit 111 of the mother chip 110 is designed as an incomplete or insufficient circuit, and is thus so designed that its output signal is fed only to the bump 130 for connection to the daughter chip 120, and not to the external connection pad 112 on which the test probe is pressed. For this reason, the internal circuit 111 of the mother chip 110 cannot be subjected to functional checking by an ordinary method.
It is of course possible to conduct functional checking by pressing the test probe to the bump 130. However, in general, such a bump 130 is provided in an inner region on the chip surface, and therefore it is not easy to press the test probe thereon accurately.
It is also possible to conduct functional checking by feeding the signal fed to the bump 130 further to another pad so that the signal can be monitored at that pad. However, this inevitably requires extra pads, and, where there are many signal lines to be monitored, requires even a larger chip size. Thus, this method is difficult to practice.
An object of the present invention is to provide a semiconductor device that is functionally complemented or enhanced by another semiconductor device and that nevertheless allows easy functional checking of itself without provision of extra pads.
Another object of the present invention is to provide a semiconductor device that is built by combining together a plurality of semiconductor chips and that nevertheless allows easy functional checking of the individual semiconductor chips before they are assembled together.
To achieve the above objects, according to one aspect of the present invention, a semiconductor device is provided with a semiconductor substrate, a circuit formed on the semiconductor substrate so as to achieve a desired function by being connected to and thereby functionally complemented or enhanced by another semiconductor device having a predetermined function, a device-to-device connection portion formed on the semiconductor substrate so as to connect the circuit to the other semiconductor device having the predetermined function, an external connection portion formed on the semiconductor substrate so as to allow input/output of a signal from/to a device other than the other semiconductor device, and a switcher formed on the semiconductor substrate so as to switch between a state in which the circuit is disconnected from the external connection portion and a state in which the circuit is connected to the external connection portion.
In this configuration, even though the internal circuit of the semiconductor device is designed as an incomplete or insufficient circuit that achieves a practical function only when functionally complemented or enhanced by the other semiconductor device, and is thus of a kind that is not usually connected directly to the external connection portion, the switcher permits the internal circuit to be connected to the external connection portion. This makes it possible to conduct functional checking of the internal circuit itself independently of the other semiconductor device having the predetermined function, and in addition by the use of the external connection portion, which facilitates such functional checking.
According to another aspect of the present invention, a semiconductor device is provided with a first semiconductor chip having a first circuit, a second semiconductor chip having a second circuit that functionally complements or enhances the function of the first circuit, a device-to-device connection portion for connecting the first and second circuits to each other, an external connection portion formed on the first semiconductor chip so as to allow input/output of a signal from/to a device other than the second semiconductor chip, and a switching circuit formed on the first semiconductor chip so as to switch between a state in which the first circuit is disconnected from the external connection portion and a state in which the first circuit is connected to the external connection portion.
In this configuration, even though the first internal circuit formed on the first semiconductor chip is designed as a practically incomplete or insufficient circuit that needs to be functionally complemented or enhanced by the second internal circuit formed on the second semiconductor chip, and is thus of a kind that is not usually connected directly to the external connection portion, the switching circuit permits the first internal circuit to be connected to the external connection portion. This makes it possible to conduct functional checking of the first semiconductor chip independently without connecting it to the second semiconductor chip.